JPH0245595A - Synthetic lubricating oil - Google Patents

Abstract

PURPOSE:To obtain a synthetic lubricating oil having high viscosity index, excellent low-temperature fluidity, stability to thermal oxidation containing a complex ester comprising a specific aliphatic polyhydric alcohol, a specific bifunctional fatty acid and a specific monofunctional fatty acid. CONSTITUTION:The aimed lubricating oil containing a complex ester comprising (A) 4-12C aliphatic polyhydric alcohol (e.g., trimethylolpropane or pentaerythritol) having 2-6 (preferably 3-4) primary hydroxyl groups, (B) 16-28C (preferably 16-24C) bifunctional fatty acid (e.g., 7-ethyloctadecane diacid or eicosane diacid and (C) 2-24C (preferably 6-18C) monofunctional fatty acid (e.g., caprylic acid or lauric acid).

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a new synthetic lubricating oil, and more specifically, a synthetic lubricating oil that has excellent properties such as a high viscosity index, low-temperature fluidity, and thermo-oxidative stability. It is related to.

[Problems to be solved by conventional techniques and inventions] In recent years,
The conditions for using lubricating oils are becoming more severe due to demands for longer oil replacement periods and energy savings, as well as higher performance of machinery and equipment, and there is a strong demand for lubricating oils with particularly excellent lubricating properties and thermo-oxidative stability. It is becoming more and more common.

In order to meet these demands, polyα-olefin,
Polybutenes, polyalkylene glycols, alkylbenzenes, alkylnaphthalenes, aliphatic diesters, polyol esters, phosphoric acid esters, etc. have been developed and used as synthetic lubricating oils. For example, polyα-olefin is used in automobile engine oil, gear oil, grease base oil, etc., polybutene is used in 2-cycle engine oil, compressor oil, etc., polyalkylene glycol is used in brake oil, hydraulic oil, etc., and alkylbenzene is used in electrical insulation oil. , refrigerating machine oil, etc., aliphatic esters are used in jet engine oil,
Automotive engine oil, hydraulic oil, grease base oil,
Phosphate esters are used in precision machine oils, etc., and phosphate esters are used in hydraulic oils, etc.

Among them, the amount of aliphatic esters used has gradually increased in recent years. For example, dibasic acid esters such as diisodecyl adipate and diisotridecyl adipate are used in oil agents and engine oils, and have the advantage of having a very low pour point, but they also have poor thermal oxidative stability and are It has the disadvantage of being highly swellable.

Among the so-called hindered esters, trimethylolpropane trioleate is widely used as a flame-retardant hydraulic fluid. Although this ester has a very high viscosity index, it has poor thermal oxidative stability due to the presence of unsaturated bonds. Further, medium chain fatty acid esters of hindered alcohols such as trimethylolpropane tricaprate and pentaerythritol tetracabrilate are used in engine oils and grease base oils.

Although this ester has excellent thermal stability, it has poor low-temperature fluidity and viscosity index, and generally only low-viscosity products can be obtained. To solve this problem, complex esters have been devised in which the viscosity is increased by partially crosslinking with adipic acid or the like.

This allows a wide viscosity range to be obtained, but polyα
- It has poor compatibility with hydrocarbon-based lubricating oils such as olefins, and its solubility in additives is also poor, which is a drawback.

Thus, thermo-oxidative stability, low temperature fluidity, high viscosity index,
A synthetic lubricating oil that satisfies well-balanced compatibility with other lubricating oils and additives has not yet been obtained.

Under the above-mentioned circumstances, the present invention has a high viscosity index, excellent thermo-oxidative stability, low-temperature fluidity, and rubber swelling property,
The purpose is to provide a synthetic lubricating oil that has excellent compatibility with other lubricating oils and additives.

[Means to solve the problem]

The present inventors have conducted intensive research to solve the above problems, and as a result, they have discovered that a complex ester having a specific structure can achieve the purpose, and have arrived at the present invention.

That is, the present invention has a primary hydroxyl group of 2 to 6 and a carbon number of 4 to 12.
The present invention provides a synthetic lubricating oil characterized by containing a complex ester consisting of an aliphatic polyhydric alcohol, a divalent fatty acid having 16 to 28 carbon atoms, and a monovalent fatty acid having 2 to 24 carbon atoms. .

Here, as the aliphatic polyhydric alcohol having 2 to 6 primary hydroxyl groups and 4 to 12 carbon atoms constituting the complex ester of the present invention, neopentyl glycol, trimethylolpropane, penquerythritol, dipenequerrythritol, trimethylol Examples include ethane and trimethylolnonane. In particular, those having 3 to 4 primary hydroxyl groups are preferred.

The monovalent fatty acids constituting the complex ester of the present invention include fatty acids derived from fats and oils, synthetic fatty acids obtained by paraffin oxidation method, oxo method, Kotsuho method, gelation method, alkali melting method, etc. Among them, those having 2 to 24 carbon atoms can be used, but those having 6 to 18 carbon atoms are preferable. Examples of these fatty acids include caproic acid, caprylic acid, enanthic acid, 2-ethylhexanoic acid, pelargonic acid, capric acid, lauric acid, myristic acid, balmitic acid, stearic acid, oleic acid, 2-heptylundecanoic acid, etc. can be mentioned. From the viewpoint of thermal oxidative stability, saturated fatty acids are particularly preferred. Also,
From the viewpoint of low-temperature fluidity, in the case of straight chain fatty acids having 13 or more carbon atoms, it is preferable to use them together with branched fatty acids.

The divalent fatty acids constituting the complex ester of the present invention include divalent fatty acids having 16 to 28 carbon atoms (e.g., eicosane dioic acid, 7-ethyl octadecane dioic acid, 7,12-
(dimethyleicosanedioic acid, dodecenylsuccinic acid, etc.) can be used, but those having 16 to 24 carbon atoms are more preferable.

From the viewpoint of low-temperature fluidity, those with a branched structure are particularly preferable.
In addition, the viscosity index improves as the number of carbon atoms in the main chain increases.

These aliphatic polyhydric alcohols, monovalent fatty acids having 2 to 24 carbon atoms, and divalent fatty acids having 16 to 28 carbon atoms can each be used singly or as a mixture of two or more, and each equivalent of the aliphatic polyhydric alcohol , 0 monovalent fatty acids having 2 to 24 carbon atoms
．． 1 to 0.998 equivalents, preferably 0.6 to 0.96 equivalents, 0.001 to 0.45 divalent fatty acids having 16 to 28 carbon atoms
It is good to react an equivalent amount, preferably 0.02 to 0.2 equivalent. The esterification reaction can be carried out in the same manner as the usual esterification reaction between carboxylic acid and alcohol.

In addition to the above-mentioned complex esters, the lubricating oil of the present invention contains mineral oils commonly used in lubricating oils, polyalpha-olefins, polybutenes, alkylbenzenes, alkylnaphthalenes, polyalkylene glycols, polyol esters, aliphatic diesters, phosphorus. Synthetic oils such as acid esters and polyphenyl ethers, or mixed oils thereof may be blended. However, the synthetic oils used are not limited to those mentioned above. The weight ratio of the complex ester to other lubricating oil components in the lubricating oil of the present invention is preferably within the range of complex ester/other lubricating oil components -10010 to 1/99.

Furthermore, various commonly used additives such as antioxidants, extreme pressure agents, rust inhibitors, antifoaming agents, and demulsifiers can be added to the lubricating oil of the present invention, if necessary.

Examples of antioxidants include phenolic antioxidants (for example, 2,6-di, monobutyl-4-methylphenol, 4,
4'-methylenebis (2,6-di-butyl-phenol), etc.), amine antioxidants (e.g. p, p'-dioctyl phenylamine, monooctyldiphenylamine, phenothiazine, 3,7-sioctylphenothia) gin, phenyl-1-naphthylamine, phenyl-2-naphthylamine, alkylphenyl-1-naphthylamine, alkylphenyl-2-naphthylamine, etc.), sulfur-based antioxidants (e.g., alkyl disulfides, thiodipropionic acid esters, benzothiazole, etc.) ), zinc dialkyldithiophosphate, zinc diallyldithiophosphate, etc. can be used.

As the extreme pressure agent, zinc dialkyldithiophosphate, zinc diallyldithiophosphate, dialkyl polysulfide, triallyl phosphate, trialkyl phosphate, etc. can be used. As the rust preventive agent, alkenylsuccinic acid, alkenylsuccinic acid derivatives, sorbitan monooleate, pentaerythritol monooleate, glycerin monooleate, amine phosphate, etc. can be used.

As antifoaming agents, silicone oil (for example, dimethylpolysiloxane, etc.), organosilicates (for example, diethylsilicate, etc.), etc. can be used. Also, those that can be used as demulsifiers include polyoxyalkylene glycol, These include polyoxyalkylene alkyl ether, polyoxyalkylene alkyl amide, polyoxyalkylene fatty acid ester, etc. However, they are not limited to the above.

The amount of these additives is usually 0.01 to 1 of the total amount of lubricating oil.
It is used in a range of 5% by weight. Further, the synthetic lubricating oil according to the present invention can be blended with an emulsifier or a dispersant, emulsified and dispersed in water, and used as a water-based lubricant.

The lubricating oil of the present invention is a hydraulic oil, metal working oil, compression oil, grease base oil, heat transfer oil,
It can be used as engine oil, turbine oil, turbocharger oil, etc., and is particularly effective in fields where high-temperature stability and lubricity are required.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

Example 1 2! A four-hole flask was equipped with a stirrer, a thermometer, a nitrogen inlet tube, and a dehydration tube with a condenser.

320 g of trimethylolpropane, 156.7 g of 7-ethyl octadecanedioic acid, and 891.5 g of caprylic acid were placed in the flask, and an esterification reaction was carried out at 230''C under a nitrogen stream for 10 hours to obtain the ester of the present invention.

Examples 2 to 5 and Comparative Examples 1 to 6 Various esters were obtained in exactly the same manner as in Example 1 using the various alcohols and acids shown in Table 1.

Test Example I The viscosity, viscosity index, pour point, additive solubility, and rubber swelling properties of the esters obtained in Examples 1 to 5 and Comparative Examples 1 to 6 were examined by the following methods.

The results are shown in Table 1.

(a) Viscosity and viscosity index "Kinematic viscosity test method for crude oil and petroleum products and method for calculating viscosity index of petroleum products" specified in JIS K-2283.

(b) Pour point: According to "Pour point of crude oil and petroleum products and cloud point test method of petroleum products" specified in JIS K-2269.

(c) Additive Solubility Ashless dispersant, metallic detergent, and zinc dialkyldithiophosphate were mixed in predetermined amounts, and the solubility of the additive was determined based on the degree of turbidity. ? The one who understands is O,? Items that are not understood are marked with an x.

(d) Rubber swelling properties According to the "vulcanized rubber physical test method" specified in JIS K-6301.

Test Example (2) The high-temperature cleanliness, thermal and oxidation stability of the esters obtained in Examples 1 to 5 and Comparative Examples 1 to 6 were investigated by the following method.

The results are shown in Table 2.

(a) Hot tube test A hot tube tester manufactured by Komatsu Equipment Co., Ltd. was used for the hot tube test. The temperature of the vertically erected glass tube was maintained at 300°C, and a small amount of test oil and air were flowed from below at the prescribed flow rates for 16 hours, and the state of the deposit formed on the inner wall of the glass tube was evaluated using a standard color scale ( (10 points on a scale of 0 to 10).

(b) Panel caulking test U.S. Federal Test Standard (No. 791 Method 34)
62), the panel temperature is 320°C1.
The test was conducted for 3 hours at a test oil temperature of 100'C, with repeated splashing for 15 seconds and stopping for 45 seconds. The thermal stability of the test oil was evaluated based on the weight of the deposit attached to the aluminum panel.

(c) Lubricating oil oxidation stability test The "lubricating oil oxidation stability test method" specified in JIS K-2514 was used. Increase in kinematic viscosity of lubricating oil after testing,
The oxidative stability of the test oils was evaluated by the increase in acid value and the increase in acid value.

Table 2 Test Example ■ The lubricity of the esters obtained in Examples 3 and 4 and Comparative Examples 1 and 3 was tested three times using the Fa lex test shown below.

The results are shown in Table 3.

<Falex test> A mixture of each base oil and ester shown in Table 3, or a base oil alone containing an ashless dispersant, a metal detergent, zinc dialkyldithiophosphate, an antioxidant, a friction modifier, and a viscosity index improver. The test was conducted using a mixture of predetermined amounts of each as a sample.

In the measurement, after a break-in operation of 200 lb for 3 minutes, the load was increased by 501 lb per minute, and the load was increased from 1000 lb to 100 lb per minute, and the value of the load at the time of seizing was taken as the lubricity index.

Table 3 [Effects of the Invention] As shown in Test Examples I to H, the complex ester of the present invention has the same viscosity as compared to the comparative product, and also has excellent low-temperature fluidity, solubility of additives, and swelling in rubber. It can be seen that it has excellent properties in terms of properties, heat and oxidation stability, and high-temperature cleanliness. Furthermore, as shown in Test Example (2), the complex ester of the present invention was poor in lubricity.

Applicant's agent Kaoru Furutani

Claims (1)

[Claims] An aliphatic polyhydric alcohol having a primary hydroxyl group of 2 to 6 and a carbon number of 4 to 12, a divalent fatty acid having a carbon number of 16 to 28, and a carbon number of 2
A synthetic lubricating oil characterized by containing a complex ester consisting of ~24 monovalent fatty acids.